Question

The following questions are case-based questions. Read the passage carefully and answer the questions that follow:

Carbohydrates are optically active polyhydroxy aldehydes and ketones. They are also called saccharides. All those carbohydrates which reduce Fehling's solution and Tollen's reagent are referred to as reducing sugars. Glucose, the most important source of energy for mammals, is obtained by the hydrolysis of starch. Vitamins are accessory food factors required in the diet. Proteins are the polymers of α-amino acids and perform various structural and dynamic functions in the organisms. Deficiency of vitamins leads to many diseases.

Answer the following:

(a) The penta-acetate of glucose does not react with Hydroxylamine. What does it indicate? (1)

(b) Why cannot vitamin C be stored in our body? (1)

(c) Define the following as related to proteins: (2)

1. Peptide linkage
2. Denaturation

OR

(c) Define the following as related to carbohydrates: (2)

1. Anomers
2. Glycosidic linkage

Answer 1

(a) D-glucose pentaacetate does not react with hyroxylamine (NH₂OH). This is due to the lack of an aldehyde group and the open chain structure.

(b) Because vitamin C is water soluble, it dissolves in water and is eliminated from the body through the urine. As a result, the body cannot store vitamin C.

(c) (i) Peptide linkage [–CO–NH–] is a peptide bond which is formed between two amino acids.

(ii) Protein found in a biological system with a unique three-dimensional structure and biological activity is called a native protein. When a protein in its native form, is subjected to physical change like change in temperature or chemical change like change in pH, the hydrogen bonds are disturbed. Due to this, globules unfold and helix get uncoiled and protein loses its biological activity. This is called denaturation of protein.

OR

(c) (i) Anomers are cyclic monosaccharides or glycoside epimers that differ in the configuration of C-1 if they are aldoses or C-2 if they are ketoses. The epimeric carbon in anomers is referred to as anomeric carbon or anomeric centre.

(ii) The two monosaccharides are joined together by an oxide linkage formed by the loss of a water molecule. Such a linkage between two monosaccharide units through an oxygen atom is called glycosidic linkage.